1. Field of the Invention
The present invention relates to a charged particle beam device, more particularly to a charged particle beam device preferable for detecting signal particles scattered in a sample and transmitted through the sample distinctively from signal particles transmitted through the sample without being scattered to obtain a sample image due to an atomic number difference from the signal particles scattered in the sample and transmitted through the sample.
2. Description of the Related Art
In a charged particle beam device represented by a scanning electron microscope, a charged particle beam thinly converged is scanned on a sample to obtain desired information (e.g., a sample image) from the sample. Much of such charged particle beam devices is used in valuation of a semiconductor device and analysis of defects. Since miniaturizing and multilayer-structuring of the semiconductor device have yearly advanced, a technique of forming the device into a thin film to evaluate the device becomes important in order to analyze defects of the multilayer-structured device.
During observation of a thin film sample, a transmission signal transmitted through the sample is usually used, but in recent years, it has been known that a transmission signal (dark-field signal) scattered in the sample and transmitted through the sample is effective for the analysis of the defects of the device, because the signal intensely reflects an atomic number contrast of the sample.
Moreover, also in a material field, in order to impart functionality, the dark-field signal which intensely reflects the atomic number contrast is also effective for grasping a dispersed state of ultra-fine particles (e.g., a catalyst) carried on fine particles.
In Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-214065 corresponding to U.S. Patent Publication No. US2004/0183017A1), there is proposed a device including a mechanism which changes a position of a detector of charged particles scattered in the sample and transmitted through the sample. In this technique, the detector of the dark-field signal can vertically be moved with respect to an incident electron track to change a signal detection angle of the transmission signal (dark-field signal) scattered in the sample and transmitted through the sample.
The dark-field signal changes in accordance with situations (an atomic number, a density of the sample, a thickness, a crystal orientation, etc.) and observation conditions (an acceleration voltage of an electron beam or the like, the detection angle or the like of the dark-field signal, etc.). Therefore, even when the same sample is observed, the image which intensely reflects the atomic number contrast is not constantly obtained. In the invention disclosed in Patent Document 1, there is not any means for clearly specifying whether or not the image based on the obtained dark-field signal has an appropriate contrast.